The purpose of this study is to determine the effects of exercise training on skin blood flow during exercise in the heat. It was hypothesized that 1) endurance exercise training will improve the age-related decrement in skin blood flow response to an exercise heat stress, 2) adaptations in the active vasodilator system will facilitate these improvements and 3) increasing daily activity (resistance training) will not provide a stimulus of sufficient magnitude to improve the skin blood flow response. Forty-one participants, young (18-30 yr) and older (>60 yr), were divided into three treatment groups: 1) aerobic training, 2) resistance training, and 3)sedentary control. Participants underwent an exercise/heat stress protocol. Following this protocol, participants completed 16 weeks of either aerobic or resistance training. An additional group of subjects (control) maintained their normal lifestyle. After 16 weeks, a second exercise/heat stress protocol was performed. Bretylium tosylate was locally iontophoresed to block vasoconstrictor activity at 2 sites on the right forearm allowing for isolation of the active vasodilator system. Laser-Doppler flowmetry probes were placed on a bretylium site and a control site to measure cutaneous blood flow on the participant's right arm. Venous occlusion plethsymography was used to quantify forearm blood flow changes in the participant's left arm. Esophageal temperature was used as an index of core temperature, and skin temperature was measured at 4 sites. Subjects cycled on a recumbent cycle ergometer for 60 min at 60% VO2max at an ambient temperature of 36 degrees C dry bulb and 24 degrees C wet bulb (relative humidity 40%). Following the exercise period, thermostatically heated probe holders were used to locally heat the two areas of the right forearm at the laser-Doppler sites. A site specific maximum was obtained which was then used to report cutaneous blood flow as a percentage of maximum. The aerobic training group worked between 60 % and 80 % of their maximal heart rate for 30 to 60 minutes per session throughout the 16 weeks, and the resistance training group trained at 60 % of their 1 repetition maximums. The control group did not partake in any training regimen. Most of the participants have completed both pre- and post-testing. In the future, we may invite some participants back to study the effects of de-training on skin blood flow.